Hydrocarbon oils used to produce high value products such as lubricating oils, turbine oils, white oils, refrigerator oils and other specialty oils are subjected to numerous treating processes including distillation, vacuum distillation, dewaxing, extraction, etc. in order to produce the final desired products.
Extraction is practiced so as to remove undesirable materials from the oils. The undesirable materials are aromatics and polar compounds which are detrimental to the stability of the oil.
Extraction processes utilizing n-methyl-2-pyrrolidone have been found to produce oils of extremely satisfactory make-up. The process, however, is marked by the extraction plant itself being susceptible to corrosion duet to the acidic components present in the oil which over time become concentrated in the NMP solvent or to acidic components inadvertently introduced into the NMP from other sources, such as cooling water leaks, etc.
To overcome the corrosion problem, various solutions have been offered.
GB No. 2,088,850 teaches that the acids and/or chloride contaminants present in NMP can be removed using basic ion-exchange resins. The acid and/or chloride contaminant level can be kept low by continuous or semi-continuous treatment. The entire volume of NMP is contacted with the ion exchange resin.
U.S. Pat. No. 4,490,240 teaches that plant corrosion can be reduced by contacting the NMP streams with a sacrificial metal which metal possesses an electrochemical potential higher than that of the metal used in the construction of the process equipment. In this way the contaminants are converted into non-corrosive species which can pass harmlessly through the plant or be removed in the extract product.